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Resistance of HDPE materials against crack propagation from two-parametric fracture mechanics point of view
Bareš, Pavel ; Fiedler, L.
The influence of geometry constraint on the resulting values of fracture characteristics of HDPE material is analysed. To this aim the crack growth resistance (J-R) curves and the initial fracture toughness values for HDPE material were experimentally determined for an arc-shaped test specimen with and without protective layer. Two parameter fracture mechanics is applied and transferability of the experimental data to the two-layer pipe used in praxis is discussed. Finite element calculations were used for the investigation. It is concluded that the estimation of the service life of pipes based on the approach is conservative.
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Crack tip opening determination for a crack terminating at the bimaterial interface
Bareš, Pavel ; Knésl, Zdeněk
In the paper the method suggested by Irwin for the crack tip opening displacement (CTOD) determination in homogeneous materials is generalized and the analytical expression for the CTOD in the case of a crack with its tip at the interface of two different materials is presented. The obtained results are used to formulate the condition of stability of a crack terminating at the interface. The suggested method is applied herein on the critical stress calculation in a case of the through-cracked protective coating. The numerical calculations are performed by finite element method (system ANSYS)
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Study of crack growing through an interface of two different materials based on analysis of crack profile in the vicinity of crack tip
Bareš, Pavel
Paper describes a numerical study of a crack penetrating the interface between two different elastic materials. The stability conditions of a crack terminating at the interface are formulated. The method introduces herein for these purposes is based on the assumption that the crack will start to propagate through the interface into the second material M2 when the shape of the crack face in the immediate vicinity of the crack tip will correspond to that in the same sample but made of purely homogeneous material M2. The numerical calculations are performed on the sample with surface protective layer under the small scale yielding conditions. The resulting critical stresses are compared with those obtained by other approaches. All results are in qualitative agreement. This method should be applicable in cases of larger crack-tip plastic deformations as well, where so far known methods are not able. All numerical calculations are performed by finite element method (system ANSYS).
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Crack stability analysis of the crack in surface protective layers based on crack mouth opening displacement
Bareš, Pavel
Paper deals with stability analysis of a crack in a coating on a substrate. It is considered that the crack is perpendicularly oriented to the interface between the coating and the substrate and the crack tip lies directly on the material interface. The simple method based on crack mouth opening displacement parameter CMOD is proposed here for a critical stress calculation in the case of through coating crack in very thin coatings. The method is then applied herein on the model example and the critical stresses for different material combinations of the coating and the substrate are calculated. Note that under these stresses the crack will start propagate across the interface to the substrate. All calculations are performed by a finite element method FEM in the system ANSYS.
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Determination of threshold values of components with protective layers
Náhlík, Luboš ; Bareš, Pavel
The contribution is focused on the influence of existing fatigue cracks in protective layers on fatigue life of structures with protective layers. The problem is solved under conditions of linear elastic fracture mechanics with help of finite element method. Is shown, that in the case of the hard protective layer on the ductile substrate represents existing crack with its tip on the bi-material interface dangerous singular stress concentrator, because of decrease of threshold values of applied loading necessary for crack propagation. Knowledge of crack propagation in protective film is of paramount importance when studying potential failure of the substrate.
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Crack propagation analysis in multilayered pipes
Bareš, Pavel
The fracture behavior of multilayered pipes applied for water and gas distribution is analyzed in this paper. The attention is focused on numerical modeling of crack propagation through twolayered pipe. Special attention is paid to the influence of interface between the layers on fatigue crack growth. The analysis is performed under the assumption of validity of linear-elastic fracture mechanic. Numerical calculations are performed by finite element method (system ANSYS).
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